When worms crossbreed, male gametes can render partners almost sterile or even kill them
When nematodes have sex with the wrong species, sperm can turn into rampaging killers.
In the worst mixed-up couplings between tiny, eyeless worms of the genus Caenorhabditis, the sperm of males from more sexually competitive species can be so aggressive they reduce the fertility of, or eventually kill, the receiving partner. The marauding sperm push beyond normal receptacles for sperm and storm into ovaries and the rest of the partner’s reproductive tract, says Eric Haag of the University of Maryland, College Park.
That premature contact with sperm can ruin eggs that have not developed enough for fertilization. Then aggressive sperm can “bust out of the ovary and start crawling around the body cavity,” Haag says. He’s even found sperm barging around in a partner’s head.